My experience has been that MC+4 starts to get challenging in terms of screentime and scene framing (easy to leave a player just sitting there for an hour at a time, if you're not careful!).
I also like the relationship map complexity that comes of so many players at one table, but it starts to become a balancing act. If you run a game where the characters are at odds with one another, or pointed at each other ("PvP"), and the MC can largely sit back and just let them do things with/against each other, then it can work really nicely.